I am in the process of studying right now. I have heard that just by reading Blueprints and maybe the little green "Current Clinical Strategies - Psychiatry" book is plenty to do quite well on the shelf.
I didn't think it was that difficult at all. I read parts of BRS, did pretest and blueprints Q&A for step 2 psych A&L psych and got a 94 raw (which frankly I'm really embarassed about as I want to do surgery and got a worse score on that shelf after studying 3-4 times as much!!) Drugs are important. I thought the most important thing was knowing the characteristics of the diagnosis (i.e. be very familiar with the dsm 4 criteria). Also, know the difference between similar diagnoses (i.e. depression vs. adjustment syndrome) Others have said knowing how certain medical disorders present as psych dx is also important (ie fat embolus gets you confused, hypothyroidism as depression, etc).
i'm studying for it right now. i've got blueprints, pretest, plat vignettes and an old lange "review of general psych"---which is soooooo long... i've never seen the little green book around. my school wants an 84 to honor (i have no idea if they give us raw scores or percentiles, but we only get one number back, more likely raw)